Income Taxes - Reconciliation of U.S Statutory Rate (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Income Tax Disclosure [Abstract]
Tax at federal statutory rate	$ (9,947)	$ (11,007)	$ (7,902)
State taxes, net of federal benefit	(1,958)	(2,270)	(1,582)
Permanent differences	(8,489)	(4,731)	289
Loss on Series C warrant liability	0	5,330	2,500
Change in valuation allowance	22,164	12,797	6,197
General business credits	(1,268)	(319)	136
Other	(491)	208	376
Provision for income taxes	$ 11	$ 8	$ 14